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Make a solution of 4 grams stannous chloride in 10 c.c. cone,
hydrochloric acid, add I gram of methyl orange dissolved in a
few drops of hot water, and boil for a few minutes until the red
colour disappears. On cooling a crystalline precipitate consist-
ing of sulphanilic acid and dimethyl /-phenylenediamine is
deposited. In order to separate the base, dilute with water, add
caustic soda solution until the precipitate of stannous hydrate
redissolves, shake out the cold solution with ether, and de-
hydrate over potassium carbonate. On distilling off the ether,
the dimethyl /-phenylenediamine remains as a crystalline
solid ; m. p. 41, On warming with dilute sulphuric acid and
lead peroxide the odour of quinone is readily perceived
(see p. 192). It also gives the (methylene blue' reaction, like
nitrosodimethylaniline (see p. 158). See Appendix, p. 289.

Potassium Benzenesulphonate, C6H5.SO3K + iH2O
Mitscherlich, Pogg. Ann., 1834, 31, 283 and 364; Michael,
Adair, Bar., 1877, 10, 585.
60 c.c. benzene.
60      cone, sulphuric acid.
The benzene and sulphuric acid are heated together on a
sand-bath in a round flask ( litre) with upright condenser.
The mixture is kept at a gentle boil with frequent shaking (an
apparatus like that shown in Fig. 78, p. I475 with mechanical
stirrer is preferable) until the top layer of benzene has Jpeen
nearly absorbed by the sulphuric acid (six to eight hours)/" On
cooling, the dark-coloured liquid is poured into cold water
(t litre) contained in a large basin, boiled up and neutralised
with powdered chalk or thick milk of lime. The massjs                       Jp
filtered'hot through a porcelain funnel or cloth from the ]|re-                      |
cipitate   of calcium   sulphate,   washed   with   hot   water   and                       J
somewhat concentrated. The solution, which contains the
calcium salt of benzene sulphonic acid, is treated with just
sufficient potassium carbonate solution to precipitate the calcium                      |! |
as carbonate and convert the sulphonic^acid into the potassium                      l||
COHEN'S ADV, p. o. c.                                               N